1. Field of the Invention
The present invention relates to drill bits and nozzles used in conjunction with drill bits for use in the drilling of oil well bores or other earth drilling applications.
2. Description of the Related Art
Rotary drill bits are well known in the art and typically comprise a drill bit body upon which are mounted cutting elements made of a hard material such as tungsten carbide or diamond. The drill bit bodies are typically provided with nozzle passages for circulating drilling fluid from the interior of the drill bit toward the point where the cutting elements engage the bottom of the bore hole.
Nozzles, both of removable and fixed construction, may optionally be attached to the lower side of a drill bit body and at the end of the nozzle passages for facilitating the jetting of drilling fluid through the passages at the bottom of the hole, thereby providing both a lubrication function in addition to assisting in the carrying away of loose debris and other cut material.
It is recognised in the art that the drilling fluid is very abrasive as it jets through the nozzles and accordingly hard materials have been employed in the past for constructing drill bit nozzles. Such materials have been required to withstand high drilling fluid jet velocities and high pressure differentials across the nozzles.
In our co-pending British Patent Application Number GB9930287.9 there is described a drill bit body which is made substantially of a material that may be drilled through by standard or conventional earth bore drilling equipment. Such technologies may be beneficial when, for example, it is desired to drill with casing and it is desired to leave the drill bit in the bore hole during the cementing of a first section of casing. After the cementing has been complete, a further and smaller diameter drill bit may be employed to extend the well bore and to do this the subsequent drill bit is required to drill through the first drill bit employed.
However, this technology has not been possible until now if the first or earlier drill bit comprised nozzles as nozzles, previously, have required to be made of a hard material for reasons described above that would resist any subsequent attempt to drill through the nozzles.
It is an object therefore of the present invention to provide drill bit nozzles that are constructed to withstand the abrasive and erosive impact of jetted drilling fluid, while also being suitable for subsequent drilling operations intended to drill through drill bit bodies to which the nozzles are attached, and indeed the nozzles themselves.
A further object of the present invention is to provide a method of drilling a well bore, wherein the drilling method is that commonly known as drilling with casing and wherein subsequent drilling may be undertaken by a subsequent drill bit, without the requirement of the removal of the earlier or first drill bit from the well bore, and wherein the earlier or first drill bit includes nozzles.
Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.